This invention relates to key controlled tumbler locks.
Various attempts to make a lock pickproof by complicating its tumbler mechanism have been made. Basically, lock manipulation is still practical because the way in which the tumbler couple and travel clearances are presented under torque remains unimproved. It would be desirable to provide an arrangement of lock tumblers that form couple and travel clearances in a way that cannot be so easily detected. It would also be worthwhile to prevent reverse picking, which is made possible when one tumbler can be returned from beyond alignment back to alignment independently of other tumblers, as by separate springs.
Winn U.S. Pat. No. 151,461 attempts to provide a pickproof lock, and shows pronged notched pin tumblers returned to misalignment by a single spring. There is no teaching of the necessity of dragging the travel of tumblers to alignment, and the complex arrangement of the curved prongs of the tumblers appears to render the lock inoperative. Also, it is basic to the design thereof that the bits of the key be brought out of contact with all but one of the tumblers during operation of the lock by the key.
Buchanan-Wollaston U.S. Pat. No. 2,302,414 shows an axial lock in which split-pin tumblers are adjacent together in the same chamber. A separate means independent of the key is necessary to move the plug relative to the cylinder after the key has aligned the tumblers. Such a means can be used to torque the lock to assist in picking.
Heyer U.S. Pat. No. 1,498,035 and Wise U.S. Pat. No. 1,696,829 each show differing ways of arraying split-pin tumblers in the same chamber. Neither array develops couple and travel clearances in a manner that is difficult to detect.
Clark U.S. Pat. No. 1,401,044 shows an axial lock in which block-pin tumblers are together adjacent in the same chamber. Basic design of block-pin tumblers requires a chamber of non-constant axial cross section.
Crepinsek U.S. Pat. No. 3,393,542 shows split-pin tumblers together adjacent within communicating chambers, each tumbler being driven by a spring that may be regarded as being located offset from a common tumbler chamber within a recess that intersects the chamber. These spring recesses intersect each other, and no means are shown for preventing entangling of the adjacent springs other than blind holes in the cylinder pins.
Scherbing U.S. Pat. No. 3,903,720 is a typical contemporary prior art axial lock construction that proposes to prevent easy manipulation of split-in tumblers by having the lock key couple to the plug via the key bits and tumblers.